Multiply stage ratios
For each stage divide driven teeth by driver teeth. Multiply those ratios to obtain the overall reduction. A 20-to-60 stage followed by a 15-to-45 stage gives 3 × 3 = 9, so a 1,500 rpm input becomes about 166.67 rpm. The tool retains the unrounded values while calculating.
State the actual topology
A compound train has the driven gear of one stage connected to the next driver on the same shaft. A simple chain of idler gears is different: intermediate tooth counts cancel from the overall ratio. Do not enter every visible gear as an independent reduction stage.
Track direction and losses
An external mesh reverses direction; an internal mesh preserves it. Two external stages therefore restore input direction. Torque rises with reduction but falls with losses. Enter defensible efficiency estimates and label them as assumptions rather than treating ideal torque as measured performance.
Enter the two-stage worked example
Choose Compound gear train, enter 1,500 rpm and 10 N·m, then use the rows 20 | 60 | external | 97 and 15 | 45 | external | 97. Each row is driver teeth, driven teeth, mesh type and efficiency percent. The first stage produces 500 rpm and 29.1 N·m; the second produces about 166.667 rpm and 84.681 N·m.
Overall efficiency is 0.97 × 0.97 = 0.9409, not 97 percent. The overall reduction is 9:1 and two reversals restore the original direction. The report and stage CSV make each intermediate result visible, which helps catch a mistaken row before passing the calculation onward.
Avoid using this model for moving carriers
This calculation assumes fixed-axis stages coupled by shafts. A planetary train with a moving carrier needs relative-speed equations and cannot be represented by simply multiplying visible tooth ratios. An idler can change direction without adding an independent reduction. Draw the shaft connections first and identify what physically drives the next stage; tooth counts alone do not establish the topology.